In 2371, Harry Kim and B'Elanna Torres used a magneton scan to examine subspace fractures which were present on a planet in the Delta Quadrant as a result of a massive polaric ion explosion. The scan results indicated that, unlike most shock waves which dissipate into the future, the shock wave from the polaric ion explosion dissipated into the past, creating subspace fractures which could allow for time travel. The timeline in which these events took place was later negated when Captain Janeway managed to change history by ensuring that the explosion never took place. (VOY: "Time and Again")